1. Field of the Invention
The present invention relates to a water-in-oil type (hereinafter abbreviated as W/O type) emulsified composition useful as a cosmetic or ointment base. More specifically, it relates to a water-in-oil type emulsified composition having specific features whereby a range of oils from polar oils to non-polar oils can be widely employed as the oil component which becomes the outer phase and the emulsified composition obtained has an excellent temperature stability and usability.
The present invention also relates to a water-and polyhydric alcohol-in-oil type emulsified composition useful as a cosmetic or ointment base. More specifically, it relates to a water- and polyhydric alcohol-in-oil type emulsified composition having specific features whereby a silicone oil can be used as the oil component which becomes the outer phase, and the emulsified composition obtained has an excellent temperature stability. In the second aspect of the present invention, the composition is not referred to as a water-in-oil type emulsified composition or polyhydric alcohol-in-oil type emulsified composition, because the inner phase of this emulsion composition comprising the main component exists in the region bridging the region of water and the region of polyhydric alcohol, and therefore, neither expression is adequate. Accordingly, the term water- and polyhydric alcohol-in-oil type emulsified composition denotes an emulsified composition containing both water and a polyhydric alcohol in the oil phase.
2. Description of the Related Art
In the prior art, to obtain a W/O type emulsified composition, a lipophilic surfactant having a HLB value of 1 to 12, for example, a polyhydric alcohol fatty acid ester type surfactant such as glycerine fatty acid ester, sorbitan fatty acid ester, etc., is used as the emulsifier, this surfactant is added in an amount of about 0.4 to 5.0 g into the oil phase, to be dissolved therein by heating to about 70.degree. to 80.degree. C., and the aqueous phase heated to about the same temperature is then added, followed by stirring by a homomixer, etc., to obtain a W/O type emulsified composition (hereinafter called W/O type emulsion).
Nevertheless, the W/O type emulsion thus obtained has a drawback in that a system having an excellent temperature stability and usability can be obtained only with difficulty, compared with the oil-in-water type (hereinafter called O/W type) emulsion. For example, with regard to the temperature stability, a separation of the oil phase, which is the continuous phase, may occur due to an agglomeration of water droplets at a low temperature. This oil phase separation also occurs at a high temperature, in that water droplets are combined, and thus have an increased particle size, and precipitated to form a sediment lower layer, and thus the upper layer consists of only the oil phase. With regard to usability, since the outer phase consists of an oil component, the advantages of skin protection, flexibility, etc., can be obtained in the fields of cosmetics and pharmaceuticals, although the drawbacks of stickiness during usage and a high skin barrier also exist.
In a known method for improving the temperature stability, a large amount of a wax is formulated in the oil phase, but although low temperature stability may be improved by this method, during storage at high temperature, a softening or melting, occurs of the formulated wax, and therefore, oil phase separation caused by water droplet combination cannot be alleviated, and thus another drawback of a problem of usability, such as spreading, arises.
As a method for eliminating the such usability problems, preferably a polar oil component having ester bond, as widely employed in the O/W type emulsion system, is formulated, but when the W/O type emulsifier used in the prior art is formulated, it is difficult to form a W/O type emulsion having an excellent stability in a system wherein a polar oil component is also formulated.